The invention relates to an adhesive tape having a tapelike backing comprising a nonwoven material which is thermally bonded with fusible fibres and is coated on at least one side with an adhesive, and to its use.
Adhesive tapes having a tapelike backing based on wovens or stitchbonded webs are known, woven tapes having been obtainable for a relatively long time and tapes having a stitchbonded web backing being described, for example, in DE U 94 01 037. Pressure-sensitive adhesive coatings are preferably employed as the adhesive coating.
DE 44 42 092 describes such an adhesive tape, based on stitchbonded web, which is coated on the reverse of the backing. DE 44 42 093 is also based on the use of a web as backing for an adhesive tape; in this case, a cross-laid fibre web is described which is reinforced by the formation of loops from the fibres of the web; i.e. a web known to the person skilled in the art as Malifleece. DE 44 42 507 likewise discloses an adhesive tape for cable bandaging, but bases it on so-called Kunit or Multikunit webs.
DE 195 23 494 C discloses the use of an adhesive tape having a backing comprising nonwoven material for bandaging cable harnesses, the said tape being coated on one side with an adhesive. The web employed in accordance with the invention is a spunbonded web of polypropylene, which is thermally consolidated and embossed with the aid of a calender, the embossing roll having an embossing surface of from 10% to 30%, preferably 19%.
DE 298 04 431 likewise discloses the use of an adhesive tape having a backing comprising nonwoven material for the bandaging of cable harnesses, the proposed spunbonded web consisting of polyester.
DE 298 19 014 U1 discloses adhesive tapes based on a web which is consolidated with air and/or water jets. The disadvantage of this backing, despite the mechanical consolidation, is that it is impossible by this technique to rule out the extraction of individual long threads and an adverse effect on the adhesive properties. In the case of very extensive consolidation of the individual fibres, other advantageous backing properties, especially for the harnessing of cables in cars, can no longer be obtained.
Adhesive tapes having a woven backing satisfy stringent technical requirements but are laborious to produce, are expensive, and have a tendency for the adhesive composition to strike through. Adhesive tapes having stitchbonded web backings, although simple in their construction, nevertheless show considerable disadvantages in practical use, such as problems owing to the heterogeneous web structure with reinforcing parallel stitches. Furthermore, the production rate of this technology is limited even with modern high-performance units.
Furthermore, with a single-sided adhesive tape having a conventional Malifleece as backing material, i.e. a Malifleece not thermally bonded, it is necessary to treat the reverse in order to prevent delamination of the backing and/or extraction of individual fibres or tufts of fibres from the surface, especially in the course of unwinding from the roll. Alternatively, this objective can be obtained by introducing a release paper between the individual plies of adhesive tape during the winding operation of the adhesive tape roll. In the case of stitchbonded or otherwise mechanically consolidated webs (needlefelts or air and/or water jet consolidated webs), the individual fibres of the web, although mechanically consolidated (stitched), are nevertheless still displaceable with respect to one another and can be torn out individually under stresses. This applies both to fibres in the sheetlike backing and, quite particularly, to fibres at the surfaces.
Unless additional improvements are ensured at this point in the production process of backing and/or adhesive tape, the fibres torn out during the unwinding of the adhesive tape roll have a marked adverse effect on the adhesive properties of the adhesive tape. They are responsible for poor visual qualities and may even ruin the entire functional capacity of the adhesive tape.
The object on which the present invention is based is therefore to improve an adhesive tape in such a way that the disadvantages of the prior art do not occur to the same extent if at all.
This object is achieved by means of an adhesive tape as specified in the main claim. The subclaims relate to advantageous developments of the adhesive tape and to a particularly advantageous use thereof.
The invention accordingly provides an adhesive tape having a tapelike backing of nonwoven material, which is coated on at least one side with an adhesive, the nonwoven web being a staple fibre web which in a first step is mechanically consolidated, or else a wet-laid web which is laid hydrodynamically, between 2% and 50% of the fibres of the web being fusible fibres, in particular between 5% and 40% of the fibres of the web.
The web is characterized in that the fibres are wet-laid or, for example, a staple fibre web is consolidated by the formation of loops from fibres of the web or by needling, stitching or air and/or water jet treatment. A second step comprises thermal bonding, in which the strength of the web is increased further by the thermal partial melting of the fusible fibres. In this way it is also possible to achieve a marked reduction in the extraction of individual filaments from the surface, which is particularly critical for the use of adhesive tape rolls.
Consolidated webs are produced, for example, on stitch-bonding machines of the xe2x80x9cMalifleecexe2x80x9d type from Malimo and can be obtained, inter alia, from Naue Fasertechnik and from Techtex GmbH. A Malifleece is characterized in that a cross-laid web is consolidated by the formation of loops from fibres of the web.
The backing used can also be a web of the Kunit or Multikunit type. A Kunit web is characterized in that it originates from the processing of a longitudinally oriented fibre web to form a sheetlike structure which has the heads and legs of loops on one side and, on the other, loop feet or pile fibre folds, but possesses neither filaments nor prefabricated sheetlike structures. A web of this kind has also been produced for many years, for example, on stitch-bonding machines of the xe2x80x9cKunitvliesxe2x80x9d type from the company Karl Mayer, formerly Malimo. A further characterizing feature of this web is that, as a longitudinal-fibre web, it is able to absorb high tensile forces in the lengthwise direction. The characteristic feature of a Multikunit web relative to the Kunit web is that the web is consolidated on both the top and bottom sides by virtue of the double-sided needle punching. Finally, stitchbonded webs are also suitable for forming an adhesive tape of the invention. A stitchbonded web is formed from a nonwoven material having a large number of stitches extending parallel to one another. These stitches are brought about by the incorporation, by stitching or knitting, of textile filaments. For this type of web, stitch-bonding machines of the type xe2x80x9cMaliwattxe2x80x9d from the company Karl Mayer, formerly Malimo, are known.
Starting materials envisaged for the textile backing are, in particular, polyester fibres, polypropylene fibres or cotton fibres. The present invention, however, is not restricted to the aforementioned materials; rather, a large number of further fibres can be used to produce the web. The basic fibres of the web consist preferably of virgin or reclaimed polyester fibres. These fibres should be between 10 and 100 mm long and should have a linear density of from 1.5 to 5 dtex.
Needled, wet-laid or air and/or water jet consolidated webs can be obtained, for example, from Freudenberg.
As the fusible fibres of the web it is preferred to employ homopolymer and copolymer fibres, amorphous, undrawn or bicomponent fibres. They are used as binding fibres for consolidating webs, by virtue of the fact that, by thermal plastication and cooling, they bond and fix the intersections of the backing fibres. Bicomponent fibres consist of a fibre core which softens or melts at higher temperatures than the other component of the fibres, which, as the sheath, can be configured symmetrically or asymmetrically around the harder core or else in other geometries, such as side-by-side configurations. Further details can be read, inter alia, in technical books such as xe2x80x9cVliesstoffexe2x80x9d (Georg Thieme Verlag, Stuttgart, 1982) or xe2x80x9cTextiltechnikxe2x80x9d (Arbeitgeberkreis Gesamttextil, Eschborn, 1996).
Such fibres of the web consist in particular of polypropylene and/or polyethylene and also mixtures or copolymers thereof. In addition to polyolefins it is also possible to employ similarly, if required, fusible fibres based, for example, on polyester or polyamide.
For sufficient thermal bonding, generally from 10% to 30%, in particular 20%, of the fibres of the web are fusible fibres, especially fusible bicomponent fibres. The fusible fibres should, furthermore, be of the same order of magnitude in terms of linear density and length as the other fibre material.
The mechanically preconsolidated or wet-laid web is thermally bonded at a temperature above the softening point of the hot-melt adhesive component, the upper temperature and the dwell time being chosen such that the other polymer material of the other fibres undergoes no marked softening, let alone melting. For this purpose it is possible to choose temperatures from 120xc2x0 C. to 300xc2x0 C. (preferably from 120xc2x0 C. to 200xc2x0 C. and, with very particular preference, from 130xc2x0 C. to 160xc2x0 C.). Heating of the web causes the fusible fibres to flow viscidly, so that, at the contact points between the fusible fibres themselves and between the fusible fibres and the other fibres, there is wetting and an enlargement in the contact area extending to the point of coalescence, which results in a strong bond. The number and extent of the bonds can be controlled not only by appropriate selection of the polymer and of the fibre type but also, during thermal treatment, by the temperature, the period of time and, possibly, the application of pressure. Given an appropriate selection of polymer, the required energy may in principle also be provided by ultrasound, high-frequency radiation or the like.
As a result of the thermal treatment, volatile components such as fibre assistants are removed in the course of thermal bonding, giving a web having favourable fogging values, so that when a low-fogging adhesive composition is used it is possible to produce an adhesive tape having particularly advantageous fogging values.